1. Technical Field of the Invention
The present invention relates in general to wing systems for use on a vehicle in aerodynamic or hydrodynamic applications, and it more particularly relates to a low-speed, conformally stowable secondary wing system for use in high speed civil transport aircraft to optimize vehicle performance and efficiency.
2. Description of the Prior Art
Canards, including small forward-mounted secondary wings, increase the total wing surface area of an aircraft for improving the low speed lift-to-drag ratio and trim characteristics of the aircraft. While canard concepts have been used in supersonic aircraft to increase low-speed performance, these designs do not allow for optimal high-speed performance and aerodynamic efficiency.
Existing canard concepts for application to high-speed aircraft fall into two general categories: fixed non-retractable configurations, and symmetrically retractable configurations which stow into cavities within the forward fuselage. An exemplary fixed canard is used in the supersonic XB-70 Valkyrie aircraft and remains deployed throughout all phases of flight. Such fixed canards allow for increased lift capabilities and greater stability at lower speeds, thus decreasing the amount of engine thrust and noise during takeoff and landing. Because fixed canards remain exposed to the airstream at supersonic cruise speeds, their induced, profile, and skin friction drags represent significant portions of the overall drag on the aircraft. Because the economic success of a high speed civil transport aircraft is highly dependent upon reducing the cruise drag to the lowest possible level, fixed canards are not desirable in this or similar vehicles.
A hybrid concept of the fixed canard design was employed by the Beechcraft Starship 1 aircraft, which utilized relatively long and narrow, dual-position symmetric canards. At low speeds the canard is fully deployed, while at high speeds the canard is partially swept back. The canard is used in the forward position during take-off and landing to offset the negative pitching moments induced by extension of the trailing edge flaps on the main wing, while it is partially swept back to decrease drag and optimize trim characteristics at cruise speeds. While this variable geometry canard design offers a compromise between low speed performance and high speed efficiency, it is not an optimal design for high speed civil transport aircraft as the canard remains exposed to the airstream during all phases of flight.
In an attempt to optimize low speed performance and high speed efficiency, the Tupolev Tu-144 supersonic transport vehicle employed two symmetrically retractable canards which stow independently into cavities within the forward fuselage. While the retractable canard concept improves upon the problems of fixed-wing and variable geometry canards, several shortcomings remain. First, the two separate hinge and actuation systems or mechanisms required to fold and support the right and left canards add to the overall weight of the aircraft. Second, the structural complexity of the hinge and deployment/retraction actuation systems increases the probability of failure during flight. Third, although the canards are stowed quasi-conformally within cavities in the upper fuselage behind the cockpit, the overall surface smoothness of the fuselage is compromised by the presence of the canards. Fourth, the rectangular platform (e.g., wing shape) used for the Tu-144 canards is not ideal for optimum aerodynamic efficiency. While leading and trailing edge high-lift devices (e.g., slats and flaps) may be used to optimize lift characteristics, such devices further add to the structural complexity and overall weight of the canard and may increase the probability of mechanical failure.
Another aircraft designed to provide low-speed high-lift capability while maintaining high-speed efficiency is the NASA AD-1 oblique wing aircraft. This small aircraft utilizes a single, quasi-elliptical, pivotable wing which rotates about a central axis. At low flight speeds, the wing is positioned perpendicularly to the fuselage, thus providing good lift characteristics without complex high-lift systems. During high-speed flight, the wing is pivoted to form an oblique angle of up to 60 degrees with the main axis of the fuselage, thus reducing drag and increasing speed. However, because the oblique wing is the primary lifting surface of the aircraft, it is not conformally stowed during the high speed flight phase.
A movable wing is used in the pivotable mono wing cruise missile described in U.S. Pat. No. 4,842,218 to Groutage et al. The missile has a single, pivotable wing which is positionable to either a captive carry position or an extended free-flight position. While the pivotable wing described in the Groutage et al. patent may be suitable as a primary wing for a cruise missile, it is not suitable for use as a low-speed secondary wing system on a supersonic aircraft. The spring-loaded, one-way deployment mechanism described in the Groutage et al. patent is not capable of retracting the wing during flight, nor is the wing conformally stowable.
Various canard concepts that relate to the general field of the present invention are illustrated in the following patents:
U.S. Pat. No. 4,161,300 to Schwaerzler, et al.; PA1 U.S. Pat. No. 4,542,866 to Caldwell, et al.; PA1 U.S. Pat. No. 4,641,800 to Rutan; PA1 U.S. Pat. No. 4,484,700 to Lockheed; PA1 U.S. Pat. No. 4,899,954 to Pruszenski, Jr.; PA1 U.S. Pat. No. 5,071,088 to Betts; PA1 U.S. Pat. No. 5,192,037 to Moorefield; PA1 U.S. Pat. No. 5,398,888 to Gerhardt; PA1 U.S. Pat. No. 5,495,999 to Cymara; PA1 U.S. Pat. No. 5,564,652 to Trimbath;